1. Field of the Invention
The present invention relates to a multimode dielectric resonator apparatus that operates in multiple resonant modes, to a filter and a duplexer that use the resonator, and to a communication apparatus that uses the filter and/or the duplexer.
2. Description of the Related Art
Conventionally, a dielectric resonator having a dielectric core arranged in a cavity uses a mode such as a TE01xcex4 mode or a TM01xcex4 mode. In a configuration of a multistage dielectric resonator apparatus formed using the aforementioned dielectric resonators, a plurality of the dielectric cores are provided in a cavity.
In the aforementioned configuration using the single resonant mode generated in the single dielectric core, however, the overall size increases in proportion to the increase in the number of resonators. In addition, the plurality of dielectric cores must be positioned and fixed with high accuracy. This makes it difficult to manufacture dielectric resonator apparatuses, such as dielectric filters, having consistent characteristics.
The present applicant has submitted Japanese Unexamined Patent Application Publication No. 11-145704, regarding a dielectric resonator apparatus in which, while a single dielectric core is used, the multiplex number is increased. The dielectric resonator apparatus according to the above application is arranged such that, when resonant spaces are represented by x, y, and z rectangular coordinates, TMx, TMy, and TMz modes are generated in which electric-field vectors extend toward the individual x, y, and z axes, and TEx, TEy, and TEz modes are generated in which electric-field vectors form loops in the plane directions perpendicular to the individual x, y, and z axes. At most six modes can thereby be used.
In the multimode dielectric resonator apparatus according to the above-described patent application, to couple predetermined resonant modes to each other, either grooves or an opening are provided in a portion in which electric fields of two modes that will be coupled together are concentrated, perturbations are applied to the electric fields in that portion, and energy is thereby transferred between the two resonant modes. However, when the TM mode and the TE mode are coupled together in the described construction, the two modes interact perpendicular to each other, so secure coupling cannot be easily obtained. The coupling grooves or openings must be deeply formed to obtain secure coupling therebetween. However, since electric-field distributions of the individual resonant modes are thereby diverged, problems are caused in that the resonant frequencies are increased, and in addition, adjustment of the filter characteristics is difficult.
In view of the above problems, the present invention provides a multimode dielectric resonator apparatus that allows TE modes and TM modes to be securely coupled to each other without increasing the resonant frequencies and that allows the filter characteristics to be easily adjusted.
The invention also provides a filter using the aforementioned multimode dielectric resonator apparatus.
The invention further provides a duplexer that uses the aforementioned multimode dielectric resonator apparatus.
The invention also provides a communication apparatus using the above.
According to one aspect of the present invention, a multimode dielectric resonator apparatus is configured in a dielectric resonator apparatus formed by arranging a dielectric core in a conductive cavity. The dielectric core is configured of a TM-mode dielectric core portion for primarily determining resonant frequencies of TM modes so that at least one of the TM modes resonates in an operating frequency band, and other TM modes resonate at frequencies higher than the operating frequency band; and a TE-mode dielectric core portion for primarily determining resonant frequencies of TE modes so that individual ones of multiple TE modes resonate in the operating frequency band. Either the shapes of the TM-mode dielectric core portion and the TE-mode dielectric core portion, or support structures therefor, are arranged asymmetrically, and predetermined TM modes and TE modes are coupled to each other so that, in areas where electric fields of the predetermined TM-modes are distributed, TE-mode electric fields are generated, having the same directional components as those of the electric fields of the TM modes.
As described above, although neither grooves nor openings are provided for coupling the TM modes and the TE modes, secure coupling can be obtained according to the arrangement in which the TM modes and the TE modes are coupled together without causing their resonant frequencies to increase. In addition, characteristic adjustment can be easily implemented according to the arrangement made such that divergences that can be caused by the coupling grooves or openings in electric-field distributions in the individual modes are reduced; that is, according to the arrangement made such that the coupling structures between the TM modes and the TE modes do not influence other resonant modes, characteristic adjustment can be easily implemented.
In the multimode dielectric resonator apparatus, the TM-mode dielectric core portion is formed to have a plate-like shape, the TE-mode dielectric core portion is formed to have a shape protruding from an upper face and a lower face of the platelike portion. Also, the TM-mode dielectric core portion and the TE-mode dielectric core portion are arranged asymmetrically; that is, there is a difference between the upper-side protruding amount and the lower-side protruding amount. With this construction, the asymmetry can be easily arranged; the TM-mode electric-field distribution areas and TE-mode electric-field distribution areas can be separated to minimize the area in which the TM-mode electric field and the TE-mode electric field overlap; and the design procedure can therefore be simplified.
The protruding parts may have any shape as long as the five modes of interest (TMx, TMy, TMz, TEx, TEy) have substantially the same resonant frequency. For example, in a quintuple mode filter for the 2 GHz band, the respective resonant frequencies should be within about 0.1 MHZ of each other.
According to another aspect of the invention, dielectric members for supporting the TM-mode dielectric core portion and the TE-mode dielectric core portion in the cavity are arranged asymmetrically with respect to the dielectric core. That is, the support structures of the TM-mode dielectric core portion and the TE-mode dielectric core portion have asymmetry. With the asymmetry thus arranged using the support members that support the dielectric core in the cavity, the dielectric core is arranged to be asymmetric, so that the manufacture thereof can be facilitated. In addition, the divergences in the electromagnetic-field distributions in other modes whose resonant frequencies are outside the operating frequency band can be minimized.
According to a further aspect of the invention, in the multimode dielectric resonator apparatus, the TM-mode dielectric core portion and the TE-mode dielectric core portion are independently supported in the cavity, either the position of one of the dielectric core portions or the positions of both dielectric core portions can be fixed, and the TM-mode dielectric core portion and the TE-mode dielectric core portion are thereby arranged to have the asymmetry. According to this construction, the relative positional relationship between the TM-mode dielectric core portion and the TE-mode dielectric core portion and the positions thereof in the cavity can be determined after the apparatus is assembled. Alternatively, the intensity of coupling between the TM modes and the TE modes can be determined in a wide range at the time of assembly of the multimode dielectric resonator apparatus; and the coupling adjustment therefor can be implemented.
In other aspects of the invention, by coupling TM modes and TE modes according to other forms of asymmetry, indirect coupling can be easily implemented among a plurality of multimode resonators sequentially coupled to each other.
In further aspects of the invention, the TE-mode dielectric core portion is provided in a position deviating from the center of the plate-like portion, which is the TM-mode dielectric core portion, in the surface direction of the plate-like portion, thereby imparting the asymmetry thereto. According to this construction, TE modes in which electric-field vectors form an electric-field loop along the surface of the plate-like portion, which is the TM-mode dielectric core portion, are coupled to TM modes in which electric-field vectors extend perpendicular to the direction in which the TE-mode dielectric core portion is deviated.
According to a further aspect of the invention, in the multimode dielectric resonator apparatus, the dielectric core is provided in a position deviating from the center of the cavity in the surface direction of the plate-like portion, which is the TM-mode dielectric core portion, thereby imparting the asymmetry thereto. According to this construction, the electric-field vectors in TM modes in the TM-mode mode dielectric core portion are deformed, and perturbations are generated between the TM modes and TE modes forming a loop in the surface direction of the plate-like portion, thereby allowing the modes to be coupled together. Also, the position of the TE-mode dielectric core portion in the surface direction of the plate-like TM-mode dielectric core portion can be arranged asymmetrically. Therefore, manufacturing can be facilitated, and in addition, divergences in the electromagnetic fields of other resonant modes can be minimized.
According to another aspect of the present invention, a filter comprises the multimode dielectric resonator apparatus having the above-described construction, and input/output structures are coupled to predetermined resonant modes in the multimode dielectric resonator apparatus. According to this construction, the filter can be formed as a small, low-loss-type filter having multiple resonator stages provided by single dielectric core and a single cavity.
According to still another aspect of the invention, a filter comprises the above-described multimode dielectric resonator apparatus, either coaxial resonators or semicoaxial resonators that are coupled to predetermined modes, and input/output structures coupled to the aforementioned resonators. According to the abovedescribed construction, the semicoaxial resonators or the coaxial resonators are externally coupled, and secure coupling is thereby obtained by use of coupling loops to increase the band width. In addition, a spurious mode according to the aforementioned multimode dielectric resonator is minimized by use of either the semicoaxial resonators or the coaxial resonators, and the overall spurious-mode characteristics are thereby decreased. Furthermore, neither the semicoaxial resonators nor the coaxial resonators need to be securely coupled to the multimode dielectric resonator. Therefore, the input/output structures in the multimode dielectric resonator portion can be miniaturized, direct passage of signals between the input and the output can be reduced, and in addition, deterioration in characteristics due to such direct passage can thereby be prevented.
According to still another aspect of the invention, a duplexer comprises two of the aforementioned filters. According to this construction, the duplexer can be small as a whole and can be a low-loss type. The duplexer thus formed can be used as an antenna-sharing unit.
According to still another aspect of the invention, a communication apparatus either uses the aforementioned filter to permit transmission signals and reception signals to pass through a passband in a high-frequency circuit section, or uses the aforementioned duplexer as an antenna-sharing unit. According to this construction, the communication apparatus can be small overall and can be a low-loss type.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.